The human T-cell leukemia viruses (HTLV) represent a family of T-cell retroviruses with three known members. HTLV type I (HTLV-I) ha transforming activity in vitro and is etiologically linked to adult T-cell leukemia, which is known to be endemic in several parts of the world. HTLV-II is another retrovirus having transforming capacity in vitro, and has been isolated from a patient with a T-cell variant of hairy cell leukemia. HTLV-III, which has also been called lymphadenopathy-associated virus and is now known as the human immunodeficiency virus (HIV), is lytic for certain kinds of T cells and has been linked to the etiology of acquired immunodeficiency syndrome (AIDS). Unlike the HTLV-I and -II viruses, HTLV-III is not known to have in vitro transforming activity.
The diagnosis of HTLV-I infection is usually based on serum antibody response to HTLV-I peptide antigens. This usually involves an initial screening assay to identify HTLV-I antibodies, based on an enzyme immunoassay (EIA) with HTLV-I virion peptides. The assays presently used for blood screening detect about 0.5 to 0.05% HTLV-I and HTLV-II positives; of these, about 4 out of 5 are false positives. Therefore, positive sera must be further tested in a confirmatory assay, using Western blot or radioimmunoprecipitation assays which detect antibody reaction to specific HTLV-I peptide antigens.
Current blood testing procedures require confirmation tests based on immunoreaction with HTLV-I p24 gag protein and at least one of the envelope proteins gp46, gp21, or gp68. When the test antigens are prepared from virion proteins, only gp46 gives a high rate of antibody reaction with true HTLV-I seropositives. Even then, the reaction with gp46 may be detected only by additional antigen testing with a more sensitive radioimmunoprecipitation assay. The above screening and confirmation testing identifies HTLV-I and HTLV-II positives, but does not distinguish between the two HTLV viruses.
It would therefore be desirable to provide an improved method for detecting HTLV-I positive sera. In particular, the improved test should be capable of detecting all HTLV-I and HTLV-II positive sera, with a minimum number of false positives, and also be able to distinguish HTLV-I from HTLV-II positive sera.